This section provides background information related to the present disclosure which is not necessarily prior art.
A hydraulic accumulator is a device in which potential energy is stored in the form of a compressed gas or spring, or by a raised weight to be used to exert a force against a relatively incompressible fluid.
Accumulators are used in fluid power systems to accumulate energy and to smooth out pulsations. A hydraulic system utilizing an accumulator can use a smaller fluid pump since the accumulator stores energy from the pump during low demand periods. This energy is available for instantaneous use, released upon demand at a rate many times greater than could be supplied by the pump alone.
Accumulators can also act as surge or pulsation absorbers, much as an air dome is used on pulsating piston or rotary pumps. They will cushion hydraulic hammer, reducing shocks caused by rapid operation or sudden starting and stopping of power cylinders in a hydraulic circuit.
There are three principal types of accumulators, the weight loaded: piston type, the spring loaded; piston type and the gas loaded piston, bladder, diaphragm and metal bellows type. Both the weight loaded type, and spring loaded type are very seldom used today. The gas loaded types use a gas as a spring cushion in conjunction with a hydraulic fluid, the gas and fluid being separated by a thin diaphragm, bladder, piston or bellows.
Hydro-pneumatic accumulators incorporate a gas in conjunction with a hydraulic fluid. The fluid has little dynamic power storage qualities. The fluid normally used in fluid power applications can be reduced in volume only about 1.7% under a pressure of 5000 PSI. Therefore when only 2% of the total contained volume is released, the pressure of the remaining oil in the system will drop to zero. However, the relative incompressibility of a hydraulic fluid makes it ideal for fluid power systems and provides quick response to power demand.
The gas in a hydro-pneumatic accumulator is a partner to the hydraulic fluid and can be compressed to high pressures and low volumes. Potential energy is stored in this compressed gas to be released upon demand. In the piston type accumulator the energy in the compressed gas exerts pressure against the piston separating the gas and hydraulic fluid. The piston in turn forces the fluid from the cylinder into the system and to the location where useful work will be accomplished.
According to the state-of-the-art, all known types of gas charging valves for accumulators require a full discharging of the gas pressure while replacing the gas valve. In subsea blow out preventer applications for oil drilling, accumulator capacities exceeding 100 gallons are common. The discharging and recharging of such large accumulators is very time-consuming and a very critical time factor on deep water blow out preventers. Also the high amount of the gas, typically nitrogen, which is lost while replacing the valve, is very cost intensive. The aim of the present disclosure is to provide a solution to this issue.